[Ovmsdev] Duktape handling of blank metrics?

[Greg D.]

Hi folks,

Does anyone know how DukTape scripting handles math with a metric that
hasn't been updated yet? 

I have a short example script in the OBDII ECU documentation which
(should) calculate a power-per-speed metric for display on a HUD.  Seems
like it would be a useful example, and wanted to verify that it actually
works. 

OVMS> vfs cat /store/obd2ecu/10
ret1=OvmsMetricFloat("v.p.speed");
ret2=OvmsMetricFloat("v.b.power");
out = 0.0;
if(ret1 > 0) { out=ret2/ret1; }
out;

I have the module in the my Roadster, and the v.p.speed metric comes up
as 0 kph (that's good - it's parked), but the power metric isn't
provided by the car, so is blank when listing the metrics.  I expected
the code to return zero.

Instead, executing the script by asking for 'obdii ecu list' causes an
immediate crash with a stack overflow in task AsyncConsole.  If I
initialize the power metric by hand (metric set v.b.power 0), the script
runs just fine, returning 0 for the metric.

Oddly, when I first set it up on the desk (sans vehicle), so both of the
metrics were blank, executing the script didn't cause crash.

Is there a way to make the code "Roadster safe", without dummying up the
metric in, say, a startup script?  Better, is there a fix for DukTape to
handle this, or should I just increase the stack size in AsyncConsole?

Thanks,

Greg